Stealth Checks - No Line of Effect

If a monster is nearby, but there's no line of sight and no line of effect, does the PC have anyway of knowing where the monster is to target it?

So, if the PC is standing in a field, and 20' away, there is a 3' high wall that runs 60' from the PC's left to right. It is a solid, 1' thick stone wall. A M sized monster starts its turn standing up in the square in the middle and behind the wall.

Minor action: Drop to prone (behind the wall, out of sight)
Move action: Crawl along the wall to the right 3 squares (still behind the wall)

Even though the monster didn't make a stealth check, does the PC know exactly where the monster is? How about the next round if the monster does a move and a move to end up at the other (left) end of the wall?

Does the PC (Wizard) know to put a Burst 1 spell 1 square up and three squares right of center in the square behind the wall?

PCs know the location of all combatants unless they're hidden.

Hidden

A monster could be 50' away and invisible and the PC still knows exactly where they are unless the monster rolls a stealth check and the PC doesn't spot them with a passive or active check.

So the wall, in this case, basically protects the monster from all attacks which require LoS and direct LoE. Unless the monster used an action to make a stealth check, after falling prone, the PC automatically knows where the monster is. Even if making a stealth check, the PC may still know where the monster is.

Correct, if a PC's passive perception beats his stealth then they know where he's at.

If a PC doesn't beat stealth with passive, then they can use a minor action to get an active check.

If one PC knows where the monster is he can tell other PCs. The other PCs still don't know for sure but can target the correct square.